1. Field of the Invention
This invention relates to optical couplers and more particularly to optical directional couplers which are tunable to vary the output ratio between the output arms.
2. Description of the Related Art
Directional couplers are known in both integrated and fibre optics, and in general consist of one or more input lightpaths coupled to two or more output lightpaths, the degree of coupling of the light between the input lightpaths and the different output lightpaths being determined at the time of manufacture.